1. Field of the Invention
The present invention relates to devices and systems for ventilation and cooling of air within a confined habitable space. More particularly, the present invention relates to a self-contained air conditioner unit suitable for cooling a confined habitable space.
2. The Prior Art
Evaporative coolers are well known in the art. So-called "swamp coolers" utilize the thermodynamic principle of adiabatic saturation. The air to be cooled is saturated with a water mist, whose evaporation from the liquid state (mist) to vapor state takes up available heat energy from the air itself, thus lowering its temperature. In this method of direct evaporative cooling, the ambient air may be cooled in the limit to its wet bulb temperature, also known as the adiabatic saturation temperature. Except in very dry climates, direct evaporative cooling is unsuitable for sustained cooling of a confined habitable space because continuous humidification of the air causes discomfort to occupants.
There also exist in the art various methods of indirect evaporative cooling, in which an airstream is first cooled by adiabatic saturation, and then used to cool a separate, non-mixing airstream across a heat-transfer partition. The latter airstream is said to be sensibly cooled; that is, cooled without altering its absolute moisture content. Such methods enable continuous cooling and recirculation of the air within a confined habitable space without the uncomfortable effects of increasing humidity.
Additionally, the prior art includes methods of pre-cooling an intake airstream before adiabatic saturation cooling, thereby enabling the airstream to be cooled below the wet bulb temperature corresponding to its initial intake conditions. In the limit, the intake airstream can be cooled to the dew point corresponding to its initial intake conditions. With relatively dry ambient conditions at intake, that is, when the ambient relative humidity is less than 40%, the dew point may be up to 10.degree. C. below the corresponding wet bulb temperature. These methods increase the cooling capacity of the intake airstream, thus imparting a greater degree of sensible cooling to the aforementioned second airstream recirculated to and from the habitable space.
The prior art described above suffers various deficiencies in its application to air conditioning equipment for space cooling. Some of these deficiencies are described in the following paragraphs.
In some current systems, ambient air at intake is blown directly through wet-air channel, and thereby cooled by adiabatic saturation (either through application of a water mist, spray, or from wetted porous material within the channel). The wet-air channel are arranged in alternate sequence to an equal number of dry-air channels, through which a separate, non-mixing flow of room air is directed in a counter-flow or cross flow direction. This latter flow of recirculating room air is sensibly cooled by heat transfer across the partitions forming the alternative wet and dry-air channels.
The major deficiency of such systems is that since no pre-cooling is effected on the intake airstream prior to adiabatic saturation, the intake airstream can only be cooled, at the limit, to the wet bulb temperature corresponding to its condition at intake. This in turn limits its capacity to cool the secondary airstream flowing in the alternate dry-air channels. To overcome this deficiency, a majority of such systems require auxiliary methods of dehumidifying the intake ambient airstream prior to passage into the wet-air channel, thereby depressing its wet bulb temperature and increasing its usable cooling capacity. The most common methods of continuous-flow, regenerative-cycle air dehumidification utilize chemical agents such Lithium Bromide or Lithium Chloride, and are well known in the art. Invariably, such dehumidification plant is more bulky and costly than the cooling apparatus itself, and therefore imposes yet another shortcoming in the present state of the art.
Other systems in the prior art cool the intake airstream by diverting a portion of the airstream after passage through the dry-air channels, and directing the diverted portion into counter-flow wet-air channel arranged in alternate order with the dry-air channels. Such arrangements enable the intake airstream to be cooled, in the limit, to the dew point corresponding to its intake conditions, thereby increasing its usable cooling capacity. Since the portion diverted into the pre-cooling wet-air channel may be required to be as high as 50% of the original intake stream, adequate flow area must be provided in the wet-air channel for the moist airstream. Consequently, such systems suffer the design tradeoff between two detrimental factors; (i) wider channels impair heat transfer between the alternate airstreams and (ii) narrower channels cause significantly increased flow resistance, especially in the wet-air channel, thereby increasing power demand in the fan blowers.
The aforementioned systems generally channel the entire intake stream along the full length of the dry-air channels, and arrange at the outlet ends thereof to separate and divert a portion of the intake airstream into adjacent wet-air channel, causing the diverted portion to flow along the full length of the wet-air channel in a counter-flow direction to the first airstream. Such arrangements require the entire portions of the first and second airstreams to flow through substantial lengths (several hundred millimeters) of closely spaced channels in order to effect the desired degree of heat transfer. The power required in the fan blowers, and the resulting rate of airflow through the respective channels, directly determine the cooling capacity, energy efficiency, physical size, noise level, and ultimately the commercial viability of such systems. Evaporative cooling systems presently known in the art are generally deficient in respect of size/capacity/efficiency considerations, the deficiency usually resulting from design tradeoffs between (i) having sufficiently narrow channels to effect adequate heat transfer, (ii) blowing a sufficient air flowrate to attain a desired cooling capacity, and (iii) achieving an acceptable level of energy efficiency in blowing the air flowrate through the required lengths of the narrow dry-air and wet-air channel.
Most indirect evaporative cooling systems in the prior art draw intake air entirely from the outdoor ambient environment. When operating in extremely hot climatic conditions, for example, when the outside ambient dry bulb temperature exceeds 35.degree. C., such an arrangement imposes an extreme load in pre-cooling the intake airstream. To achieve the necessary degree of pre-cooling, the portion of the intake stream diverted into the wet-air channel in the counter-flow direction may exceed 50% of the original intake stream. This pre-cooling load accordingly reduces the available cooling capacity for the habitable space. Under extremely hot ambient outdoor conditions, incomplete pre-cooling of the intake stream causes many current systems to suffer a serious decline in performance.
Yet another deficiency in current indirect evaporative cooling systems rests in the type and placement of lining material affixed to the partition walls of the wet-air channel. Optimal heat transfer across the partitions between the wet and dry-air channels would be achieved in the absence of any lining material. However it is necessary to maintain a supply of water uniformly distributed across the surfaces of the wet channel walls in order to facilitate adiabatic saturation. In the present state of the art, this is achieved through the use of absorbent capillary porous material affixed to the wet side of each partition. This material serves to distribute and retain the water introduced into the wet-air channel either by a mist, drip, or wicking arrangement.
Consequently, the majority of current systems suffer a design tradeoff between two detrimental factors: (i) capillary porous material insulates the heat transfer surfaces, thereby impeding heat transfer, (ii) an absence of material results in inadequate water distribution across the surfaces, making evaporative saturation difficult to achieve. As a compromise between the aforementioned factors, some current designs utilize material arrayed in an alternating pattern on the wet side of each partition surface.